Citation: Discoasterales Hay, 1977Rank: OrderNotes & discussion: Hay (1977) described the Order Discoasterales as a broad taxonomic group that included most radial and stellate Mesozoic and Cenozoic nannoliths. It is used here as a narrower taxonomic concept that incorporates the type family, the Discoasteraceae, together with the other radially symmetrical Paleogene nannolith groups, the Heliolithaceae, Fasciculithaceae and Sphenolithaceae, which originated within four million years of one another and have common morphological features suggesting phylogenetic affinity (Bown 2010). The term discoasteralids is used here as a concise term for nannoliths produced by members of the order Discoasterales.

Farinacci & Howe catalog pages: Discoasterales [no catalog entry yet]

Distinguishing features: Radially symmetrical nannoliths formed from one to several separate cycles of elements that radiate from a common centre or axis.

Morphology remarks: Includes disc-like (discoasters), stellate (discoasters), cylindrical (fasciculiths, helioliths and sphenoliths) and conical (fasciculiths and sphenoliths) morphologies, but all with rotational symmetry about a single axis. The top and bottom surfaces, relative to the axis of rotation are usually different and one surface is normally concave and is considered proximal. All members show complex crystal units with control of both a-axis and c-axis orientation. The structures are often chiral.Evolution & Phylogeny: The earliest members of the Discoasterales appear in the Palaeocene and they show more similarities to heterococcoliths -see e.g. Aubry et al. 2011. They also share with radial symmetry and precise control of calcite crystallographic orientation and complex sculpting of individual calcite crystal units. They apparently lack however growth from a proto-coccolith ring and so presence of alternating V- and R-units. Phylogenetically it seems reasonable to infer that they evolved from heterococcoliths by modification of the biomineralisation process.

Geological Range: Last occurrence (top): near top of Gelasian Stage (85% up, 1.9Ma, in Gelasian stage). Data source: Total of range of species in this databaseFirst occurrence (base): in upper part of Danian Stage (69% up, 63Ma, in Danian stage). Data source: Total of range of species in this database